\subsection{Collaborative open-source tools}
\label{tools-collaborative}
% myonotlogy, ACTIVE semantic mediawiki ontology editor (stephan woelger), ikewiki, kiwi

The success of user generated content gave rise to ontology building tools which focus on human collaboration to generate and manage content - in this case, ontologies. We will present four open-source solutions, all of which are based on or extend the wiki principle.

\subsubsection{myOntology}
myOntology is an open ontology environment for Semantic Web based e-Commerce, which is developed by the Semantic Technology Institute (STI) Innsbruck. The myOntology research project tries to exploit the potential of human collaboration to create and manage ontologies. The techniques utilized are similar to those used by the MediaWiki\footnote{\url{mediawiki.org}} software (developed by the Wikimedia Foundation). Such an environment enables the following core features:
\begin{itemize}
  \item Automatic sharing of documents/ontologies on creation
  \item Collaborative editing
  \item History of previous modifications (revisions)
  \item Ability to link to a specific version of a document/ontology 
\end{itemize}

myOntology aims to produce the ``theoretical foundations, and deployable technology for the Wiki-based, collaborative and community-driven development and maintenance of ontologies''~\cite{myontology}. Like other community portals for creating and maintaining content (in this case ontologies), myOntology provides software which supports the community ``to keep the system clean and to find consensus on the vocabulary specifications''~\cite{myontology-primer}. \newline


myOntology offers a textual editor to manipulate ontologies. We would like to note that the version\footnote{myOntology prototype (beta), available online \url{http://myontology.sti2.at/} } we used for evaluation is a prototype which failed to work properly.  

\subsubsection{Semantic MediaWiki}
Semantic MediaWiki\footnote{\url{http://semantic-mediawiki.org/wiki/Semantic_MediaWiki}} ``is a free, open-source extension to MediaWiki [\ldots] that lets you store and query data within the wiki's pages''~\cite{mediawiki}. The current version as of writing this paper is 1.5.3, released on November 4th 2010.

The basic features are similar to the ones of MediaWiki since \textit{Semantic MediaWiki} - as stated above - extends the popular wiki software. Semantic MediaWiki introduces some additional markup into the wiki-text which allows users to add ``semantic annotations'' to the wiki.~\cite{semanticmediawiki-intro} Further, the \textit{Introduction to Semantic MediaWiki}~\cite{semanticmediawiki-intro} lists the following features as helpful for producing semantically enriched content:
\begin{itemize}
  \item Automatically-generated lists as opposed to manually managed lists in MediaWiki
  \item Visual display of information in calendars, timelines, graphs, maps, etc. 
  \item Improved data structure by utilizing MediaWiki categories
  \item Searching information by creating specific queries
  \item Inter-language consistency by decoupling data from textual descriptions
  \item External reuse of data is enabled by exporting to various formats like CSV, JSON and RDF. 
  \item Integrate and mash-up data via multiple extensions such as the \textit{Data Import}, \textit{Data Transfer} and \textit{External Data} extensions
  \item Inline queries which offers queries in a wiki-like syntax in edit mode, \linebreak e.g. \texttt{<ask>[[Category:Actor]] [[born in::Boston]]</ask>}. In view mode, the results of the query are displayed.~\cite{semantic_wikipedia}
\end{itemize}

Semantic MediaWiki is widely used by public wikis as well as organizations. Notable public wikis include the Metacafe wiki, SNPedia, SKYbrary, Metavid, MetaBase, the Math Images Project, the U.S. Department of Energy's Open Energy Information, the Sunlight Foundation's OpenCongress wiki and Break.com's Chickipedia. Organizations that use SMW internally include Pfizer, Harvard Pilgrim Health Care, Johnson \& Johnson Pharmaceutical Research and Development, the Pacific Northwest National Laboratory, the Metropolitan Museum of Art and the U.S. Department of Defense.~\cite{wiki:semantic_mediawiki}

\subsubsection*{Semantic MediaWiki Ontology Editor}
One extension of the Semantic MediaWiki is the \textit{SMW OntologyEditor}\footnote{\url{http://semantic-mediawiki.org/wiki/Help:SMW_extensions\#SMW_OntologyEditor}} which has been developed as part of the ACTIVE project\footnote{\url{http://www.active-project.eu}} and focuses on the development of lightweight ontologies (which includes vocabularies, categories, properties and elements). The \textit{SMW OntologyEditor} also provides a set of knowledge repair algorithms which should help the user to maintain a consistent knowledge base. Those repair algorithms can be reached via a set of special pages similar to MediaWiki's \textit{``special pages''}. The pages are mostly related to categories and show you categories within cycles, categories with redundant subclass relations, categories with similar property sets and categories without subcategories.

There are other special pages which can be used for maintainance purposes. It is possible to display ontology elements with similar names, category- and property histograms and a category repair tab.

Import as well as export to and from OWL/XML is possible. Special pages are presented in more detail by~\cite{smw_ontology_editor}.

\subsubsection{IkeWiki}
IkeWiki is a Java-based semantic wiki engine developed by Salzburg Research\footnote{\url{http://www.salzburgresearch.at/}}. Version 2.0 was released in March 2008 and marks the end of the development on the wiki. IkeWiki is considered as a research prototype~\cite{ikewiki} which offers basic wiki features as well as semantic formalizations for resource types, links and metadata. As representation languages RDF and OWL are used. Since IkeWiki is not actively developed anymore we won't go into further detail regarding the features of this software.

\subsubsection{Kiwi}
The Kiwi\footnote{\url{http://www.kiwi-project.eu}} (shorthand for ``Knowledge in a Wiki'') project is the successor of the previously presented IkeWiki and is actively developed by Salzburg Research. The latest release is version 1.0 (October 2010). KiWi is a \textit{Java EE} and \textit{JBoss Seam} based semantic wiki engine and won the \textit{ESWC Best Demo Award} in 2009~\cite{semwiki:kiwi}.

KiWi introduces the term ``Content Versatility'' which can be summarized as: ``Same content, different views''. The underlying principle is that every piece of information is a combination of human-readable content and associated metadata~\cite{kiwipaper}. This means that the same piece of information can be presented to the user in many different forms (as a wiki page, as a blog post, as a graphic, \ldots). This concept enables that one \textit{content item} (one ``unit of information'') can be represented in many different ways, thus becoming multiple things at the same time. The content item is the core concept of the KiWi system~\cite{kiwipaper}.

Another concept of KiWi are \textit{Extended Triples} which extend usual RDF triples with maintenance information that is used internally by the KiWi system. Extended triples are used for tasks like versioning, transactions, user- or group-associations and various other reasons. To the outside world, extended triples look like ordinary triples and can be exported into the usual Semantic Web formats like RDF~\cite{kiwipaper}.

Textual content is represented internally as XML documents that can be queried and transformed to other representations like HTML or XSL-FO (for PDF and other print formats) using standard XML query languages (XQuery, XSLT) or using the rule-based reasoning language developed in KiWi~\cite{kiwipaper}. However, said rule-based reasoning language is still in development and not much information about it has been published yet.

